| The amount of waste residue discharged from the lead zinc smelting industry is huge.Due to the low utilization rate of waste residue,most of it is directly stored for treatment,resulting in resource waste and potential harm to the environment.The treatment of smelting waste residue has become an urgent issue for the green and sustainable development of the lead zinc industry.Lead blast furnace slag is a smelting slag produced during the pyrometallurgical process of lead,characterized by high content of SiO2,CaO,Fe,and heavy metal elements.In this paper,the method of carbothermic reduction-magnetic separation is used to treat lead blast furnace slag.Pb and Zn volatilize into dust,and iron and other heavy metals remain in the reduction slag.Iron concentrate and tailings were obtained by magnetic separation of reduced slag,and heavy metals are solidified in the tailings,achieving the extraction of Pb,Zn,and Fe in the slag and the solidification/stabilization of heavy metals.The main research contents and conclusions are as follows:(1)The mineral composition and element distribution characteristics of lead blast furnace slag were studied.Fe mainly occurs in the form of magnetic iron,siderite carbonate,iron silicate,and pyrite sulfide;Pb is mainly composed of sardinianite,cerussite,galena and plumbojarosite;Zn mainly exists in the form of oxides and sulfides.Thermodynamic studies of carbothermic reduction have shown that iron compounds are reduced to metallic iron at suitable temperatures and reducing atmospheres.ZnS can be co reduced with CaO/FeO to form metallic zinc,which is volatilized in the form of metallic zinc.Pb is mainly volatilized in the form of PbO and PbS.(2)The reduction behavior of Pb,Zn,and Fe in the carbothermic reduction process of lead blast furnace slag was studied.The results showed that the volatilization rates of Pb,Zn,and the metallization rates of Fe increased with the increase of reduction temperature and time,while the amount of reducing agent had a small impact on the reduction of Pb,Zn,and Fe.Under the optimal conditions of reduction temperature 1300℃,reduction time 60 min,coke consumption 4%,and magnetic field strength 250 MT,three sets of parallel comprehensive verification experiments were conducted.The average volatilization rates of Pb and Zn are 84.78%and 95.58%,respectively.The average metallization rate and average recovery rate of iron are 98.31%and 77.46%,respectively.The main phases of dust are PbSnS2 and ZnO.Pb in the tailings is mainly embedded in silicate minerals in the form of sulfide,and elements such as Zn,As,and Cd are relatively evenly distributed in silicate minerals.(3)The study on leaching toxicity of reducing slag shows that the higher the reaction temperature,the higher the solidification efficiency of Pb,Zn,As,and Cd.With the prolongation of reaction time,the curing efficiency of Pb and Zn becomes higher,and there is no significant change in the curing effect of As and Cd.The amount of reducing agent has no significant effect on the curing effect of As and Cd.The study on the leaching toxicity of lead blast furnace slag and magnetic separation tailings shows that the leaching risk of Pb,Zn,As,and Cd from lead blast furnace slag is extremely high.The leaching values of Pb,Zn,As,and Cd from magnetic separation tailings all meet the requirements of the national standard GB5085.3-2007.The analysis of heavy metal speciation in lead blast furnace slag and magnetic separation tailings shows that the residual states of Pb,Zn,As,and Cd in lead blast furnace slag are 2.4%,4.54%,16.2%,and 26.2%,respectively.The residual states of Pb,Zn,As,and Cd in magnetic separation tailings are 24.81%,25%,29.5%,and 29.31%,respectively.The carbothermic reduction-magnetic separation method is used to treat lead blast furnace slag,resulting in product dust,iron concentrate,and magnetic separation tailings.This can preliminarily achieve efficient recovery of lead,zinc,and iron from lead blast furnace slag and effective solidification of heavy metals. |
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